Abstract: Base on the model of the authorps interior cell , the fiber t race of Chenps surface cell and the section shapeof the bundle described by Chou , et al , a new combined model including surface cells and interior cells is proposed.This model can simulate the st ructure of the three- dimensional four - step braided composites accurately. On thebasis of this model , the elastic properties of three-dimensional four- step braided composites are predicted throughthe finite element calculation. By comparing the theoretical prediction with the experimental data , the influence ofthe surface cells on the whole elastic properties was discussed. The result indicates that the surface cells are impor-tant for predicting the elastic properties of three-dimensional four-step braided composites.